Non-aqueous electrolytic solution for power storage element

ABSTRACT

in which Mn+ represents a hydrogen ion, an alkali metal ion, an alkali earth metal ion, an aluminum ion, a transition metal ion, or an onium ion, R1 and R2 are different from each other and represent a hydrocarbon group having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10 carbon atoms and having at least one of a halogen atom, a heteroatom, and an unsaturated bond, and n represents a valence.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a phosphoric acid diester salt, aproduction method therefor, a non-aqueous electrolytic solution for apower storage element, and a power storage element, and moreparticularly to a phosphoric acid diester salt which can improvecharge-discharge characteristics of a power storage element when thephosphoric acid diester salt is applied to the power storage element,and can suppress the rise in internal resistance after storage at hightemperature, a production method therefor, a non-aqueous electrolyticsolution for a power storage element, and a power storage element.

Description of the Related Art

Examples of a power storage element using a non-aqueous electrolyticsolution include secondary batteries such as a lithium ion secondarybattery, capacitors such as an electric double layer capacitor and thelike. Of these power storage elements, the lithium ion secondary batteryhas already been put to practical use widely as power sources ofportable telephones and personal computers, and demand for the lithiumion secondary battery been increasing. However, since numerous rawmaterials including expensive metals such as lithium are used in thelithium ion secondary battery, there is concern about the raw materialsthat might be supplied in response to the increase in demand.

Meanwhile, a sodium ion secondary battery has attracted much attentionas a secondary battery that solves concern about the supply of the rawmaterials, and a study has been made. The sodium ion secondary batteryhas higher Clarke number than that of lithium and uses sodium, anabundant resource, as a main constituent material, so that it isexpected that the sodium ion secondary battery contributes to solving ofconcern about the supply and cost reduction.

In these power storage elements, regarding use environment temperaturethereof, there is a need to have higher durability than conventional oneunder both high temperature environment and low temperature environment.Because of enlargement of cells under high temperature environment, thecells are steadily exposed to comparatively high temperature due to notonly use environment but also self-heating, so that an improvement indurability at high temperature is very important. When the power storageelement is stored under high temperature environment, the internalresistance of the cells rises as an electrode, an electrolytic solution,and an electrolyte deteriorate, leading to significant energy loss whichoriginates in internal resistance under low temperature environment.

In an alkali metal ion secondary battery among power storage elements,it is generally interpreted that a stable film (solid electrolyteinterface) is formed, which has alkali metal ion conductivity but has noelectron conductivity, at an interface between the electrode activematerial and the electrolytic solution. However, when the alkali metalion secondary battery is stored under high temperature environment, itsstable film sometimes causes cracking, dissolution, or decomposition,thus resulting in a problem such as deterioration of charge-dischargecharacteristics of the alkali metal ion secondary battery, or increasein impedance.

There has been proposed, as a sodium ion secondary battery among alkalimetal ion batteries, a sodium ion secondary battery in which anon-aqueous solvent of a saturated cyclic carbonate or a mixture of asaturated cyclic carbonate and a chain carbonate is used as anelectrolytic solution, and hard carbon is used as a negative electrodeactive material (Patent Document 1 mentioned below). It is mentionedthat this sodium ion secondary battery is operable at normal temperatureand can suppress deterioration of battery performance that is caused bythe negative electrode active material. However, there is a problem thatthe sodium ion secondary battery exhibits insufficient storagecharacteristics under high temperature environment and charge-dischargecharacteristics after storage deteriorate, and the internal resistancerises.

PRIOR ART DOCUMENTS Patent Documents Patent Document 1: WO 2010/109889 ASUMMARY OF THE INVENTION Problems to be Solved by the Invention

In light of the above problems, the present invention has been made andan object thereof is to provide a phosphoric acid diester salt which cansuppress deterioration of charge-discharge characteristics of a powerstorage element, and can suppress the rise in internal resistance afterstorage at high temperature, a production method therefor, a non-aqueouselectrolytic solution for a power storage element, and a power storageelement.

Solutions to the Problems

To solve the above problems, the phosphoric acid diester salt of thepresent invention is characterized by a phosphoric acid diester saltrepresented by the following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.

In the above configuration, either one of R¹ and R² is preferably analkyl group having 1 to 10 carbon atoms and having a halogen atom, andother one is preferably an alkyl group having 1 to 10 carbon atoms andhaving no halogen atom.

In the above configuration, either one of R¹ and R² is preferably a2,2,2-trifluoroethyl group, and other one is preferably an ethyl group.

In the above configuration, M is preferably at least one selected fromthe group consisting of lithium, sodium, magnesium, and calcium.

In the above configuration, M is preferably triethylmethylammonium,tetraethylammonium, 1-ethyl-3-methylimidazolium, or1-ethyl-2methylpyrrolidinium.

To solve the above problems, the method for producing a phosphoric aciddiester salt of the present invention is characterized by including thesteps of: producing a phosphoric acid diester by hydrolyzing aphosphoric acid triester represented by the chemical formula (2)mentioned below; and producing a phosphoric acid diester saltrepresented by the chemical formula (1) mentioned below by reacting thephosphoric acid diester with M^(n+)(OH)n (in which M^(n+) represents ahydrogen ion, an alkali metal ion, an alkali earth metal ion, analuminum ion, a transition metal ion, or an onium ion, and n representsa valence); wherein a —OR¹ group and a —OR² group in the phosphoric acidtriester are leaving groups, and leaving ability of the —OR¹ group islarger than leaving ability of the —OR² group:

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence: and

wherein R¹ and R² are different from each other and represent ahydrocarbon group having 1 to 10 carbon atoms, or a hydrocarbon grouphaving 1 to 10 carbon atoms and having at least one of a halogen atom, aheteroatom, and an unsaturated bond.

In the above configuration, either one of R¹ and R² is preferably analkyl group having 1 to 10 carbon atoms and having a halogen atom, andother one is preferably an alkyl group having 1 to 10 carbon atoms andhaving no halogen atom.

Either one of R¹ and R² is preferably a 2,2,2-trifluoroethyl group, andother one is preferably an ethyl group.

To solve the above problems, the non-aqueous electrolytic solution for apower storage element of the present invention is characterized byincluding, as an additive, a phosphoric acid diester salt represented bythe following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.

To solve the above problems, the non-aqueous electrolytic solution for apower storage element of the present invention is characterized byincluding, as an electrolyte, a phosphoric acid diester salt representedby the following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.

In the above configuration, either one of R¹ and R² is preferably analkyl group having 1 to 10 carbon atoms and having a halogen atom, andother one is preferably an alkyl group having 1 to 10 carbon atoms andhaving no halogen atom.

In the above configuration, either one of R¹ and R² is preferably a2,2,2-trifluoroethyl group, and other one is preferably an ethyl group.

In the above configuration, M is preferably at least one selected fromthe group consisting of lithium, sodium, magnesium, and calcium.

In the above configuration, M is preferably triethylmethylammonium,tetraethylammonium, 1-ethyl-3-methylimidazolium, or1-ethyl-2methylpyrrolidinium.

To solve the above problems, the power storage element of the presentinvention is characterized by using a non-aqueous electrolytic solutionincluding, as an additive, a phosphoric acid diester salt represented bythe following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.

To solve the above problems, the power storage element of the presentinvention is characterized by using a non-aqueous electrolytic solutionincluding, as an electrolyte, a phosphoric acid diester salt representedby the following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.

Effects of the Invention

According to the present invention, when using a phosphoric acid diestersalt represented by the chemical formula (1) as an electrolyte or anadditive in a non-aqueous electrolytic solution, it is possible toimprove charge-discharge characteristics of a power storage elementusing the non-aqueous electrolytic solution, and to suppress the rise ininternal resistance even after storage at high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view which schematically illustrates asodium ion secondary battery according to an embodiment of the presentinvention in which an additive of the present embodiment is added to anelectrolytic solution for a non-aqueous electrolytic solution.

FIG. 2 is a schematic sectional view which schematically illustrates anelectrochemical characteristics evaluation cell with a non-aqueouselectrolytic solution containing an additive for a non-aqueouselectrolytic solution of the present invention added therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (Phosphoric AcidDiester Salt)

First, a phosphoric acid diester salt according to the presentembodiment will be described below. The phosphoric acid diester salt isrepresented by the following chemical formula (1).

In the chemical formula (1), M^(n+) represents a hydrogen ion, an alkalimetal ion, an alkali earth metal ion, an aluminum ion, a transitionmetal ion, or an onium ion.

Examples of the alkali metal ion include, but are not limited to,lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion and thelike.

Examples of the alkali earth metal ion include magnesium ion, calciumion, strontium ion, barium ion and the like.

Examples of the transition metal ion include, but are not limited to,manganese ion, cobalt ion, nickel ion, chromium ion, copper ion,molybdenum ion, tungsten ion, vanadium ion and the like.

Examples of the onium ion include ammonium ion (NH⁴⁺), primary ammoniumion, secondary ammonium ion, tertiary ammonium ion, quaternary ammoniumion, quaternary phosphonium ion, sulfonium ion and the like.

Examples of the primary ammonium ion include, but are not limited to,methylammonium ion, ethylammonium ion, propylammonium ion,isopropylammonium ion and the like.

Examples of the secondary ammonium ion include, but are not limited to,dimethylammonium ion, diethylammonium ion, dipropylammonium ion,dibutylammonium ion, ethylmethylammonium ion, methylpropylammonium ion,methylbutylammonium ion, propylbutylammonium ion, diisopropylammoniumion and the like.

Examples of tertiary ammonium which forms the tertiary ammonium ioninclude, but are not limited to, trimethylammonium ion, triethylammoniumion, tripropylammoniumammonium ion, tributylammonium ion,ethyldimethylammonium ion, diethylmethylammonium ion,triisopropylammonium ion, dimethylisopropylammonium ion,diethylisopropylammonium ion, dimethylpropylammonium ion,butyldimethylammonium ion, 1-methylpyrrolidinium ion,1-ethylpyrrolidinium ion, 1-propylpyrrolidinium ion,1-butylpropylpyrrolidinium ion, 1-methylimidazolium ion,1-ethylimidazolium ion, 1-propylimidazolium ion, 1-butylimidazolium ion,pyrazolium ion, 1-methylpyrazolium ion, 1-ethylpyrazolium ion,1-propylpyrazolium ion, 1-butylpyrazolium ion, pyridinium ion and thelike.

Examples of quaternary ammonium which forms the quaternary ammonium ioninclude, but are not limited to, aliphatic quaternary ammoniums,imidazoliums, pyridiniums, pyrazoliums, pyridaziniums and the like.

Examples of the aliphatic quaternary ammoniums include, but are notlimited to, tetraethylammonium, tetrapropylammonium,tetraisopropylammonium, trimethylethylammonium, dimethyldiethylammonium,methyltriethylammonium, trimethylpropylammonium,trimethylisopropylammonium, tetrabutylammonium, trimethylbutylammonium,trimethylpentylammonium, trimethylhexylammonium,1-ethyl-1-methyl-pyrrolidinium, 1-butyl-1-methylpyrrolidinium,1-ethyl-1-methyl-piperidinium, 1-butyl-1-methylpiperidinium and thelike.

Examples of the imidazoliums include, but are not limited to,1,3dimethyl-imidazolium, 1-ethyl-3-methylimidazolium,1-n-propyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium,1-n-hexyl-3-methylimidazolium and the like.

Examples of the pyridiniums include, but are not limited to,1-methylpyridinium, 1-ethylpyridinium, 1-n-propylpyridinium and thelike.

Examples of the pyrazoliums include, but are not limited to,1,2-dimethylpyrazolium, 1-methyl-2-ethylpyrazolium,1-propyl-2-methylpyrazolium, 1-methyl-2-butylpyrazolium,1-methylpyrazolium, 3-methylpyrazolium, 4-methylpyrazolium,4-iodopyrazolium, 4-bromopyrazolium, 4-iodo-3-methylpyrazolium,4-bromo-3-methylpyrazolium, 3-trifluoromethylpyrazolium and the like.

Examples of the pyridaziniums include, but are not limited to,1-methylpyridazinium, 1-ethylpyridazinium, 1-propylpyridazinium,1-butylpyridazinium, 3-methylpyridazinium, 4-methylpyridazinium,3-methoxypyridazinium, 3,6-dichloropyridazinium,3,6-dichloro-4-methylpyridazinium, 3-chloro-6-methylpyridazinium,3-chloro-6-methoxypyridazinium and the like.

Examples of quaternary phosphonium which forms the quaternaryphosphonium ion include, but are not limited to,benzyltriphenylphosphonium, tetraethylphosphonium,tetraphenylphosphonium and the like.

Examples of the sulfonium ion include, but are not limited to,trimethylsulfonium, triphenylsulfonium, triethylsulfonium and the like.

Among those listed as M^(n+), M^(n+) is preferably lithium ion, sodiumion, magnesium ion, calcium ion, tetraalkylammonium ion,alkylimidazolium ion, or alkylpyrrolidinium ion, from the viewpoint ofavailability.

In the chemical formula (1), R¹ and R² are functional groups which aredifferent from each other. R¹ and R² represent a hydrocarbon group, or ahydrocarbon group having at least one of a halogen atom, a heteroatom,and an unsaturated bond (hereinafter referred to as “hydrocarbon grouphaving a halogen atom, etc.”). The hydrocarbon group has 1 to 10 carbonatoms, and preferably 1 to 4 carbon atoms. The hydrocarbon group havinga halogen atom has 1 to 10 carbon atoms, and preferably 1 to 4 carbonatoms. The number of unsaturated bonds is preferably in a range of 1 to10, more preferably 1 to 5, and particularly preferably 1 to 3.

Specific examples of the hydrocarbon group or the hydrocarbon grouphaving a halogen atom include chain alkyl groups such as a methyl group,an ethyl group, a propyl group, a butyl group, an isopropyl group, apentyl group, a hexyl group, a heptyl group, and an octyl group; cyclicalkyl groups such as a cyclopentyl group and a cyclohexyl group; chainhalogen-containing alkyl groups such as a 2-iodoethyl group, a2-bromoethyl group, a 2-chloroethyl group, a 2-fluoroethyl group, a1,2-diiodoethyl group, a 1,2-dibromoethyl group, a 1,2-dichloroethylgroup, a 1,2-difluoroethyl group, a 2,2-diiodoethyl group, a2,2-dibromoethyl group, a 2,2-dichloroethyl group, a 2,2-difluoroethylgroup, a 2,2,2-tribromoethyl group, a 2,2,2-trichloroethyl group, a2,2,2-trifluoroethyl group, and a hexafluoro-2-propyl group; cyclichalogen-containing alkyl groups such as a 2-iodocyclohexyl group, a2-bromocyclohexyl group, a 2-chlorocyclohexyl group, and a2-fluorocyclohexyl group; chain alkenyl groups such as a 2-propenylgroup, an isopropenyl group, a 2-butenyl group, and a 3-butenyl group;cyclic alkenyl groups such as a 2-cyclopentenyl group, a 2-cyclohexenylgroup, and a 3-cyclohexenyl group; chain alkynyl groups such as a2-propynyl group, a 1-butynyl group, a 2-butynyl group, a 3-butynylgroup, a 1-pentynyl group, a 2-pentynyl group, a 3-pentynyl group, and a4-pentynyl group; phenyl groups such as a phenyl group, a3-methoxyphenyl group, a 4-methoxyphenyl group, a 3,5-dimethoxyphenylgroup, and a 4-phenoxyphenyl group; halogen-containing phenyl group suchas a 2-iodophenyl group, a 2-bromophenyl group, a 2-chlorophenyl group,a 2-fluorophenyl group, a 3-iodophenyl group, a 3-bromophenyl group, a3-chlorophenyl group, a 3-fluorophenyl group, a 4-iodophenyl group, a4-bromophenyl group, a 4-chlorophenyl group, a 4-fluorophenyl group, a3,5-diiodophenyl group, a 3,5-dibromophenyl group, a 3,5-dichlorophenylgroup, and a 3,5-difluorophenyl group; and naphthyl groups such as a1-naphthyl group, a 2-naphthyl group, and a 3-amino-2-naphthyl group.

The halogen atom means an atom of fluorine, chlorine, bromine, oriodine. The hydrocarbon group having a halogen atom means that hydrogensin the hydrocarbon group may be partially or entirely substituted withany one of these halogen atoms. The heteroatom means an atom of oxygen,nitrogen, or sulfur. The hydrocarbon group having a heteroatom meansthat hydrogens and carbons in the hydrocarbon group may be partially orentirely substituted with any one of these heteroatoms.

Specific examples of the hydrocarbon group having a heteroatom include a2-methoxyethyl group, a 2-(2-methoxyethoxy)ethyl group, a2-(2-(2-methoxyethoxy)ethoxy)ethyl group, a2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl group and the like.

From the viewpoint of the solubility in an organic solvent having highpolarity (for example, a non-aqueous solvent such as propylene carbonateor ethylene carbonate, details will be mentioned in the description ofan additive for a non-aqueous electrolytic solution of a power storageelement according to the present embodiment), the phosphoric aciddiester anion is preferably a phosphoric acid diester anion in which ananion structure is polarized and the dipole moment as the degree ofpolarization is as high as possible. From such point of view, either oneof R¹ and R² is preferably an alkyl group having 1 to 10 carbon atomsand having a halogen atom, and other one is preferably an alkyl grouphaving 1 to 10 carbon atoms and having no halogen atom. Examples of thealkyl group having 1 to 10 carbon atoms and having a halogen atominclude a fluorine-containing alkyl group. The fluorine-containing alkylgroup is not particularly limited and may be of straight-chain,branched, or cyclic. Specific examples thereof include a trifluoromethylgroup, a 2-fluoroethyl group, a 2,2-difluoroethyl group, a2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a2,2,3,3,3-pentafluoropropyl group, a hexafluoroisopropyl group, a2,2,3,3,4,4,5,5-octafluoropentyl group, a2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl group, a3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl group and thelike. From the viewpoint of availability of the raw material, a2,2,2-trifluoroethyl group is preferable among these fluorine-containingalkyl groups. When the fluorine-containing alkyl group is a2,2,2-trifluoroethyl group, the alkyl group having 1 to 10 carbon atomsand having no halogen atom is preferably an ethyl group, from theviewpoint of availability of the raw material. The alkyl group having ahalogen atom more preferably has 1 to 4 carbon atoms. The alkyl grouphaving no halogen atom more preferably has 1 to 4 carbon atoms.

Specific examples of the phosphoric acid diester anion in which R¹ andR² are composed only of alkyl groups which are different from each otherinclude ethylmethylphosphoric acid anion, ethylpropylphosphoric acidanion, methylpropylphosphoric acid anion and the like.

Specific examples of the phosphoric acid diester anion in which eitherone of R¹ and R² is an alkyl group having a halogen atom, and the otherone is an alkyl group having no halogen atom include(2,2,2-trichloroethyl)ethylphosphoric acid anion,(2,2,2-trichloroethyl)methylphosphoric acid anion,hexachloroisopropylethylphosphoric acid anion,hexachloroisopropylmethylphosphoric acid anion,(2,2,2-trifluoroethyl)ethylphosphoric acid anion,(2,2,2-trifluoroethyl)methylphosphoric acid anion,hexafluoroisopropylethylphosphoric acid anion,hexafluoroisopropylmethylphosphoric acid anion and the like.

Specific examples of the phosphoric acid diester in which either one ofR¹ and R² is an alkyl group having a heteroatom, and the other one is analkyl group include methyl(2-methoxyethyl)phosphoric acid anion,methyl(2-(2-methoxyethoxy)ethyl)phosphoric acid anion,methyl(2-(2-(2-methoxyethoxy)ethoxy)ethyl)phosphoric acid anion,methyl(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl)phosphoric acidanion and the like.

In the chemical formula (1), n represents a valence. For example, n=1when M is a monovalent cation, n=2 when M is a divalent cation, and n=3when M is a trivalent cation.

Specific examples of the phosphoric acid diester salt represented by thechemical formula (1) include sodium ethyl methyl phosphate, sodium ethylpropyl phosphate, sodium ethyl(2,2,2-trichloroethyl)phosphate, sodiummethyl(2,2,2-trichloroethyl)phosphate, sodium ethyl hexachloroisopropylphosphate, sodium ethyl(2,2,2-trifluoroethyl)phosphate, sodiummethyl(2,2,2-trifluoroethyl)phosphate, sodiumethyl(2,2,2-trifluoroethyl)phosphate, sodium ethyl hexafluoroisopropylphosphate, sodium methyl(2-methoxyethyl)phosphate, sodiummethyl(2-(2-methoxyethoxy)ethyl)phosphate, sodiummethyl(2-(2-(2-methoxyethoxy)ethoxy)ethyl)phosphate, sodiummethyl(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl)phosphate,1-ethyl-3-methylimidazoliumethylmethylphosphoric acid,1-ethyl-3-methylimidazoliumethylpropylphosphoric acid,1-ethyl-3-methylimidazoliumethyl(2,2,2-trichloroethyl)phosphoric acid,1-ethyl-3-methylimidazoliummethyl(2,2,2-trichloroethyl)phosphoric acid,1-ethyl-3-methylimidazoliumethylhexachloroisopropylphosphoric acid,1-ethyl-3-methylimidazoliumethyl(2,2,2-trifluoroethyl)phosphoric acid,1-ethyl-3-methylimidazoliummethyl(2,2,2-trifluoroethyl)phosphoric acid,1-ethyl-3-methylimidazoliumethyl(2,2,2-trifluoroethyl)phosphoric acid,1-ethyl-3-methylimidazoliumethylhexafluoroisopropylphosphoric acid,1-ethyl-3-methylimidazoliummethyl(2-methoxyethyl)phosphoric acid,1-ethyl-3-methylimidazoliummethyl(2-(2-methoxyethoxy)ethyl)phosphoricacid,1-ethyl-3-methylimidazoliummethylmethyl(2-(2-(2-methoxyethoxy)ethoxy)ethyl)phosphoricacid,1-ethyl-3-methylimidazoliummethyl(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl)phosphoricacid, triethylmethylammoniumethylmethylphosphoric acid,triethylmethylammoniumethylpropylphosphoric acid,triethylmethylammoniumethyl(2,2,2-trichloroethyl)phosphoric acid,triethylmethylammoniummethyl(2,2,2-trichloroethyl)phosphoric acid,triethylmethylammoniumethylhexachloroisopropylphosphoric acid,triethylmethylammonium ethyl(2,2,2-trifluoroethyl)phosphoric acid,triethylmethylammoniummethyl(2,2,2-trifluoroethyl)phosphoric acid,triethylmethylammonium ethyl(2,2,2-trifluoroethyl)phosphoric acid,triethylmethylammoniumethylhexafluoroisopropylphosphoric acid,triethylmethylammoniummethyl(2-methoxyethyl)phosphoric acid,triethylmethylammoniummethyl(2-(2-methoxyethoxy)ethyl)phosphoric acid,triethylmethylammoniummethyl(2-(2-(2-methoxyethoxy)ethoxy)ethyl)phosphoricacid,triethylmethylammoniummethyl(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl)phosphoricacid and the like.

(Method for Producing Phosphoric Acid Diester Salt)

Next, a description will be made of a method for producing a phosphoricacid diester salt according to the present embodiment.

The method for producing a phosphoric acid diester salt of the presentembodiment includes at least a step A of producing a phosphoric aciddiester by hydrolyzing a phosphoric acid triester represented by thechemical formula (2) mentioned below; and a step B of producing aphosphoric acid diester salt represented by the chemical formula (1)mentioned below by reacting the phosphoric acid diester with M^(n+)(OH)n(in which M^(n+) represents, a hydrogen ion, an alkali metal ion, analkali earth metal ion, an aluminum ion, a transition metal ion, or anonium ion, and n represents a valence, hereinafter referred to as“hydroxide”).

In the chemical formula (2), R¹ and R² are as already describedhereinabove, and are the same as R¹ and R² in the chemical formula (1).Therefore, detailed description thereof is omitted.

The phosphoric acid triester can be hydrolyzed, for example, in thepresence of water. Whereby, a reaction as shown in the followingchemical scheme (1) arises to produce a phosphoric acid diester.

Furthermore, by reacting a phosphoric acid diester with the hydroxide, areaction represented by the following chemical scheme (2) arises toproduce a phosphoric acid diester salt.

The steps A and B can be performed at a time by reacting the hydroxidewith the phosphoric acid triester in the presence of water. Also in thiscase, first, as shown in the chemical scheme (1), hydrolysis between thephosphoric acid triester and water arises to produce a phosphoric aciddiester. Thereafter, as shown in the chemical scheme (2), it is presumedthat a phosphoric acid diester reacts with a hydroxide to produce aphosphoric acid diester salt. Namely, it is considered that, bysubjecting a phosphor atom of the phosphoric acid triester tonucleophilic attack by water, a phosphoric acid diester is producedfirst, and then a salt is obtained by a neutralization reaction with ahydroxide.

When the hydroxide is reacted with the phosphoric acid triester in thepresence of water to produce a phosphoric acid diester salt at a time,there is a need that leaving ability of a —OR¹ group of the phosphoricacid triester as a raw material is larger than leaving ability of a —OR²group. The reason is that the —OR¹ group of the phosphoric acid triestermust be eliminated first due to hydrolysis. Whereby, it is made possibleto obtain a phosphoric acid diester salt of the present embodiment inwhich R¹ and R² are different from each other and are arrangedasymmetrically.

The leaving ability of the —OR¹ group and the —OR² group as a leavinggroup can be roughly presumed by the pKa value of each protonated formthereof. Namely, the pKa value of H—OR¹ is preferably smaller than thatof H—OR². The pKa value can be estimated by the Bordwell pKa Table.Alternatively, it is possible to presume that those including anelectron-withdrawing group in the leaving group have high leavingability.

When the hydroxide is reacted with the phosphoric acid triester in thepresence of water to produce a phosphoric acid diester salt at a time,regarding a reaction ratio of the hydroxide to the phosphoric acidtriester, the amount of the hydroxide is preferably at least 0.5equivalent or more, more preferably 0.5 equivalent to 1 equivalent,still more preferably 0.8 equivalent to 1 equivalent, and particularlypreferably 0.9 equivalent to 0.95 equivalent, based on 1 equivalent ofthe phosphoric acid triester. When the use amount of the phosphoric acidtriester is set at 0.5 equivalent or more, it is possible to prevent thereactivity between the phosphoric acid triester and the hydroxide fromdeteriorating and to suppress the unreacted hydroxide from remaining,thus making it possible to suppress purity of the phosphoric aciddiester salt from being lowered. The upper limit of the use amount ofthe phosphoric acid triester is not particularly limited. However, theuse of the phosphoric acid triester in an excessive amount requiresproduction time and energy more than necessary when this phosphoric acidtriester is distilled off, thus resulting in an industrial disadvantage.It is therefore preferred to appropriately set the upper limit of theuse amount of the phosphoric acid triester in accordance with thereactive species or reaction scales.

When the reaction between the phosphoric acid triester and the hydroxideis started in the presence of water, the reaction starting temperatureis not particularly limited as long as the reaction proceeds and thereaction starting temperature may be appropriately set in accordancewith the reactive species. Usually, the reaction starting temperature isin a range of 0 to 200° C. From the viewpoint of the reactivity, thereaction starting temperature is in a range of 20 to 150° C., and morepreferably 40 to 120° C. When the reaction starting temperature is setat 0° C. or higher, the reaction rate can be prevented from beingremarkably attenuated. Meanwhile, when the reaction starting temperatureis set at 200° C. or lower, energy loss due to use of excess energy canbe suppressed. The method for adjusting the reaction startingtemperature is not particularly limited. When the system is cooled tocontrol so as to set the reaction starting temperature in theabove-mentioned temperature range, control can be made by ice cooling ofa reaction vessel including the phosphoric acid triester and hydroxidecharged therein. When the system is heated to control so as to set thereaction starting temperature in the above-mentioned temperature range,control can be made by an oil bath set at an arbitrary temperature.

When the phosphoric acid triester is reacted with the hydroxide in thepresence of water, the reaction time is not particularly limited, andthe reaction time may be appropriately set in accordance with thereactive species. Usually, the reaction times are preferably in a rangeof 30 minutes to 10 hours. From the viewpoint of industrial production,the reaction time is preferably in a range of 30 minutes to 5 hours, andmore preferably 30 minutes to 3 hours.

In the reaction between the phosphoric acid triester and the hydroxide,water, an organic solvent, or the phosphoric acid triester can be usedas a reaction solvent. When using an organic solvent or a phosphoricacid triester as the reaction solvent, the reaction between thephosphoric acid triester and the hydroxide is performed in a state wherewater is allowed to be present in the organic solvent or phosphoric acidtriester.

The organic solvent is not particularly limited as long the organicsolvent does not cause a trouble that the reaction solvent reacts withother reactants or reaction products. Specific examples thereof includealcohols, nitriles, esters, ketones, ethers, halogenated hydrocarbonsand the like. These organic solvents can be used alone or in combinationof two or more thereof.

Examples of the alcohols include, but are not limited to, methanol,ethanol, propanol, butanol, isopropyl alcohol, pentanol, hexanol,heptanol, octanol, 2-iodoethanol, 2-bromoethanol, 2-chloroethanol,2-fluoroethanol, 1,2-diiodoethanol, 1,2-dibromoethanol,1,2-dichloroethanol, 1,2-difluoroethanol, 2,2-diiodoethanol,2,2-dibromoethanol, 2,2-dichloroethanol, 2,2-difluoroethanol,2,2,2-tribromoethanol, 2,2,2-trichloroethanol, 2,2,2-trifluoroethanol,hexafluoroisopropyl alcohol, ethylene glycol monomethyl ether,diethylene glycol monomethyl ether, triethylene glycol monomethyl ether,tetraethylene glycol monomethyl ether and the like. These alcohols canbe used alone or in combination of two or more thereof.

Examples of the nitriles include, but are not limited to, acetonitrile,propionitrile and the like. These nitriles can be used alone or incombination of two or more thereof.

Examples of the esters include, but are not limited to, dimethylcarbonate, diethyl carbonate, ethylmethyl carbonate, ethylene carbonate,propylene carbonate, ethyl acetate, methyl acetate, butyl acetate andthe like. These esters can be used alone or in combination of two ormore thereof.

Examples of the ketones include, but are not limited to, acetone, methylethyl ketone, methyl isobutyl ketone, cyclohexanone and the like. Theseketones can be used alone or in combination of two or more thereof.

Examples of the ethers include, but are not limited to, diethyl ether,tetrahydrofuran, dimethoxyethane and the like. These ethers can be usedalone or in combination of two or more thereof.

Examples of the halogenated hydrocarbon include, but are not limited to,dichloromethane, chloroform and the like. These halogenated hydrocarbonscan be used alone or in combination of two or more thereof.

Other examples of the organic solvent include nitromethane, nitroethane,dimethylformamide and the like.

The use amount of the organic solvent is preferably at least 1 time,more preferably 1 to 200 times, still more preferably 1 to 100 times,and particularly preferably 1 to 50 times, the mass of the phosphoricacid triester. When the use amount of the organic solvent is adjusted atat least 1 time the mass of the phosphoric acid triester, it is possibleto prevent the reactivity between the phosphoric acid triester and thehydroxide from deteriorating and to suppress the unreacted hydroxidefrom remaining, thus making it possible to suppress yield and purity ofthe phosphoric acid diester salt from being lowered. The upper limit ofthe use amount of the organic solvent is not particularly limited.However, the use of the organic solvent in an excessive amount requiresenergy more than necessary when this solvent is distilled off, thusresulting in an industrial disadvantage. It is therefore preferred toappropriately set the upper limit of the use amount of the organicsolvent in accordance with the reactive species.

The use amount of water as the reaction solvent is preferably 0.5equivalent or more, and more preferably 1 equivalent or more, based on 1equivalent of the phosphoric acid triester. When the use amount of wateris set at 0.5 equivalent or more, it is possible to prevent thereactivity between the phosphoric acid triester and the hydroxide fromdeteriorating and to suppress the unreacted hydroxide from remaining,thus making it possible to suppress purity of the phosphoric aciddiester salt from being lowered. The upper limit of the use amount ofwater is not particularly limited. However, the use of water in anexcessive amount requires production time and energy more than necessarywhen this water is distilled off, thus resulting in an industrialdisadvantage. It is therefore preferred to appropriately set the upperlimit of the use amount of water in accordance with the reactive speciesor reaction scales.

When water is contained in the organic solvent as the reaction solventor the phosphoric acid triester, the content of water is preferably in arange of 0.5 equivalent to 100 equivalents, more preferably 1 equivalentto 50 equivalents, and still more preferably 1 equivalent to 10equivalents, based on 1 equivalent of the phosphoric acid triester. Whenthe content of water is set at 0.5 equivalent or more, it is possible toprevent the reactivity between the phosphoric acid triester and thehydroxide from deteriorating and to suppress the unreacted phosphoricacid triester from remaining, thus making it possible to suppress purityof the phosphoric acid diester salt from being lowered. Meanwhile, whenthe content of water is set at 100 equivalents or less, it is possibleto suppress energy required to remove excess water.

When using an organic solvent as the reaction solvent, the order of theaddition of a phosphoric acid triester, a hydroxide, and water is notparticularly limited. When using water as the reaction solvent, theorder of the addition of a phosphoric acid triester and a hydroxide isnot particularly limited. When using a phosphoric acid triester as thereaction solvent, the order of the addition of water and a hydroxide isnot particularly limited.

Regarding the phosphoric acid diester salt obtained by the method of thepresent embodiment, it is also possible to produce a phosphoric aciddiester salt having desired different kinds of cations by performingcation exchange utilizing the solubility, or cation exchange using anion exchange resin.

It is also possible to produce a phosphoric acid diester by reacting thephosphoric acid diester salt obtained by the method of the presentembodiment with Arrhenius acid such as sulfuric acid or hydrochloricacid. It is also possible to obtain a phosphoric acid diester byperforming proton exchange using an ion exchange resin. It is alsopossible to produce a phosphoric acid diester salt by reacting thephosphoric acid diester obtained by this method with a halide or ahydroxide.

In the present embodiment, immediately after the step of producing aphosphoric acid diester salt, the step of purifying the phosphoric aciddiester salt may be performed. By subjecting the phosphoric acid diestersalt to cation exchange, purification can be performed immediately afterthe step of producing a phosphoric acid diester salt having differentkinds of cations. Immediately after reacting the phosphoric acid diesterwith the halide to produce a phosphoric acid diester salt, purificationcan be performed. The purification method is not particularly limited,and it is possible to employ a method by an operation such asdistillation or drying, or a method using an adsorbent such as activecarbon or an ion exchange resin. Purity of the phosphoric acid diestersalt can be enhanced by performing such purification.

(Method for Producing Phosphoric Acid Triester)

It is possible to produce a phosphoric acid triester represented by theabove chemical formula (2) serving as a starting material of thephosphoric acid diester salt of the present embodiment by variousmethods.

For example, the phosphoric acid triester can be produced by reacting amonohalophosphoric acid diester represented by the following chemicalformula (3) with a hydroxy compound in the other organic solvent or inthe absence of a solvent:

wherein R¹ is the same as defined in the chemical formula (1), and Xrepresents I, Br, Cl or the like.

Examples of the hydroxy compound include, but are not limited to,alcohols, phenols, naphthols, saccharides and the like. These hydroxycompounds listed may be appropriately selected in accordance with inaccordance with the usage of the phosphodiester salt, which is anintended product. From the viewpoint of availability, among thesehydroxy compounds, alcohols can be suitably used.

Examples of the alcohols include, but are not limited to, chain alkylalcohols such as methanol, ethanol, propanol, butanol, isopropylalcohol, pentanol, hexanol, heptanol, and octanol; cyclic alkyl alcoholssuch as cyclopentanol and cyclohexanol; chain halogen-containingalcohols such as 2-iodoethanol, 2-bromoethanol, 2-chloroethanol,2-fluoroethanol, 1,2-diiodoethanol, 1,2-dibromoethanol,1,2-dichloroethanol, 1,2-difluoroethanol, 2,2-diiodoethanol,2,2-dibromoethanol, 2,2-dichloroethanol, 2,2-difluoroethanol,2,2,2-tribromoethanol, 2,2,2-trichloroethanol, 2,2,2-trifluoroethanol,and hexafluoroisopropyl alcohol; cyclic halogen-containing alkylalcohols such as 2-iodocyclohexanol, 2-bromocyclohexanol,2-chlorocyclohexanol, and 2-fluorocyclohexanol; chain alkenyl alcoholssuch as 2-propenol, isopropenol, 2-butenyl alcohol, and 3-butenylalcohol; cyclic alkenyl alcohols such as 2-cyclopenten-1-ol,2-cyclohexen-1-ol, and 3-cyclohexen-1-ol; chain alkynyl alcohols such as2-propynyl alcohol, 1-butynyl alcohol, 2-butynyl alcohol, 3-butynylalcohol, 1-pentynyl alcohol, 2-pentynyl alcohol, 3-pentynyl alcohol, and4-pentynyl alcohol; and alcohols having a hetero element, such asethylene glycol monomethyl ether, diethylene glycol monomethyl ether,triethylene glycol monomethyl ether, and tetraethylene glycol monomethylether. It is preferred to appropriately select from among these alcoholssuch that the leaving ability of the —OR¹ group becomes larger than theleaving ability of the —OR² group. These alcohols can be used alone orin combination of two or more thereof.

The other organic solvent is not particularly limited, and it ispreferred to use the hydroxy compound or an aprotic organic solvent.When using a hydroxy compound as the other organic solvent, it ispreferred to use a hydroxy compound which is the same as the hydroxycompound as a raw material. When using, as the other organic solvent, ahydroxy compound which is different from the hydroxy compound as a rawmaterial, the side reaction may cause production of those other thandesired phosphoric acid triester, leading to lowered yield.

Examples of the aprotic organic solvent include, but are not limited to,nitriles, esters, ketones, ethers, halogenated hydrocarbons and thelike. These aprotic organic solvents can be used alone or in combinationof two or more thereof.

The use amount of the other organic solvent is preferably at least 2times, more preferably 2 to 100 times, and still more preferably 2 to 50times, the mass of the monohalophosphoric acid diester. When the useamount of the other organic solvent is adjusted at at least 2 times themass of the monohalophosphoric acid diester, the reaction between themonohalophosphoric acid ester and the hydroxy compound can beefficiently performed. The upper limit of the use amount of the otherorganic solvent is not particularly limited. However, the use of theorganic solvent in an excessive amount requires energy more thannecessary when this organic solvent is distilled off, thus resulting inan industrial disadvantage. It is therefore preferred to appropriatelyset the upper limit of the use amount of the organic solvent inaccordance with the reactive species.

The use amount of the hydroxy compound as the raw material is preferablyin a range of 1 equivalent to 5 equivalents, more preferably 1equivalent to 3 equivalents, and still more preferably 1.05 equivalentsto 1.1 equivalents, based on 1 equivalent of the monohalophosphoric aciddiester. When the use amount of the hydroxy compound is set at 1equivalent or more, it is possible to prevent the monohalophosphoricacid diester as the raw material from remaining. The upper limit of theuse amount of the hydroxy compound is not particularly limited. However,the use of the hydroxy compound in an amount of more than 5 equivalentrequires energy more than necessary when the excess hydroxy compound isdistilled off. It is therefore preferred to appropriately set the upperlimit of the use amount of the hydroxy compound in accordance with thereactive species.

When the reaction between the monohalophosphoric acid diester and thehydroxide is started, the reaction starting temperature is notparticularly limited as long as the reaction proceeds. Usually, thereaction starting temperature is in a range of −20° C. or higher and200° C. or lower, preferably 15° C. or higher and 100° C. or lower, andmore preferably 0° C. or higher and lower than 50° C. When the reactionstarting temperature is set at 200° C. or lower, it is possible tosuppress yield of the hydroxy compound from lowering due to vaporizationand to prevent purity of the phosphoric acid triester as the productfrom lowering. Meanwhile, when the reaction starting temperature is setat −20° C. or higher, it is possible to prevent the monohalophosphoricacid diester from solidifying. The method for adjusting the reactionstarting temperature is not particularly limited. When the system iscooled to control so as to set the reaction starting temperature in theabove-mentioned temperature range, control can be made by ice cooling ofa reaction vessel including the monohalophosphoric acid diester andhydroxide charged therein. When the system is heated to control so as toset the reaction starting temperature in the above-mentioned temperaturerange, control can be made by an oil bath set at an arbitrarytemperature. After completion of the reaction between themonohalophosphoric acid ester and the hydroxy compound, the temperaturedecreases to about room temperature.

It is also possible to produce the phosphoric acid triester by using adihalophosphoric acid monoester represented by the following chemicalformula (4) in place of the halophosphoric acid diester. Also in thiscase, reaction can be performed in the other organic solvent or in theabsence of a solvent:

wherein R² is the same as defined in the chemical formula (1), and Xrepresents I, Br, Cl or the like.

The use amount of the other organic solvent is preferably at least 2times, more preferably 2 to 100 times, and still more preferably 2 to 50times, the mass of the dihalophosphoric acid monoester. When the useamount of the other organic solvent is adjusted at at least 2 times themass of the dihalophosphoric acid monoester, the reaction between thedihalophosphoric acid monoester and the hydroxy compound can beefficiently performed. The upper limit of the use amount of the otherorganic solvent is not particularly limited. However, the use of theorganic solvent in an excessive amount requires energy more thannecessary when this organic solvent is distilled off, thus resulting inan industrial disadvantage. It is therefore preferred to appropriatelyset the upper limit of the use amount of the organic solvent inaccordance with the reactive species.

The use amount of the hydroxy compound is preferably in a range of 2equivalents to 10 equivalents, more preferably 2 equivalents to 6equivalents, and particularly preferably 2.05 equivalents to 3equivalents, based on 1 equivalent of the dihalophosphoric acidmonoester. When the use amount of the hydroxy compound is set at 2equivalents or more, it is possible to prevent the dihalophosphoric acidmonoester from remaining. The upper limit of the use amount of thehydroxy compound is not particularly limited. However, the use of thehydroxy compound in an amount of more than 10 equivalent requires energymore than necessary when the excess hydroxy compound is distilled off.It is therefore preferred to appropriately set the upper limit of theuse amount of the hydroxy compound in accordance with the reactivespecies.

When the reaction between the dihalophosphoric acid monoester and thehydroxy compound is started, the numerical range of the reactionstarting temperature is the same as in case where the monohalophosphoricacid diester is reacted with the hydroxy compound.

It is also possible to react a monohalophosphoric acid diester or adihalophosphoric acid monoester with a hydroxy compound in the hydroxycompound in place of the other organic solvent in the presence of abase. In this case, the use amount of the hydroxy compound as thereaction solvent is the same as that of the other organic solvent.Examples of the base include, but are not limited to, triethylamine andthe like.

The content of the base is preferably in a range of 1 equivalent to 5equivalents, more preferably 1 equivalent to 3 equivalents, and stillmore preferably 1.05 equivalents to 2 equivalents, in the case of amonohalophosphoric acid diester. When the content of the base is set at1 equivalent or more, it is possible to prevent the reactivity betweenthe monohalophosphoric acid diester and the hydroxide from deterioratingand to suppress the unreacted monohalophosphoric acid diester ordihalophosphoric acid monoester from remaining, thus making it possibleto suppress purity of the phosphoric acid triester from being lowered.Meanwhile, when the content of the base is set at 5 equivalent or more,it is possible to prevent consumption of energy required to removeexcess base.

The content of the base is preferably in a range of 2 equivalents to 10equivalents, more preferably 4 equivalents to 6 equivalents, and stillmore preferably 2.1 equivalents to 4 equivalents, in the case of adihalophosphoric acid monoester. When the content of the base is set at1 equivalent or more, it is possible to prevent the reactivity betweenthe monohalophosphoric acid diester and the hydroxide from deterioratingand to suppress the unreacted monohalophosphoric acid diester ordihalophosphoric acid monoester from remaining, thus making it possibleto suppress purity of the phosphoric acid triester from being lowered.Meanwhile, when the content of the base is set at 10 equivalents ormore, it is possible to prevent consumption of energy required to removeexcess base.

It is also possible to react a monohalophosphoric acid diester or adihalophosphoric acid monoester with a hydroxy compound in the presenceof a catalyst of a metal halide or in the absence of a catalyst. In thiscase, the reaction is preferably performed under reflux conditions. Whenthe reaction is started, the reaction starting temperature is notparticularly limited as long as the reaction proceeds. Usually, thereaction starting temperature is in a range of 40° C. or higher and 300°C. or lower, preferably 60° C. or higher and 250° C. or lower, and morepreferably 80° C. or higher and lower than 200° C. When the reactionstarting temperature is set at 40° C. or higher, the by-producedhydrogen halide can be efficiently removed. Meanwhile, when the reactionstarting temperature is set at 300° C. or lower, excess energy used forthe reaction can be suppressed. The method for adjusting the reactionstarting temperature is not particularly limited. When the system iscooled to control so as to set the reaction starting temperature in theabove-mentioned temperature range, control can be made by ice cooling ofa reaction vessel including the monohalophosphoric acid diester ordihalophosphoric acid monoester and the hydroxy compound chargedtherein. When the system is heated to control so as to set the reactionstarting temperature in the above-mentioned temperature range, controlcan be made by an oil bath set at an arbitrary temperature. Aftercompletion of the reaction between the monohalophosphoric acid diesteror dihalophosphoric acid monoester and the hydroxy compound, thetemperature decreases to about room temperature.

The metal halide is not particularly limited and, for example, sodiumchloride, magnesium chloride and the like can be used. When using thecatalyst of the metal halide, the use amount of the metal halide ispreferably in a range of 0.01 equivalent to 0.5 equivalent, morepreferably 0.01 equivalent to 0.2 equivalent, and still more preferably0.01 to 0.1 equivalent, based on the monohalophosphoric acid diester ordihalophosphoric acid monoester.

(Additive for Non-Aqueous Electrolytic Solution of Power StorageElement)

The phosphoric acid diester salt of the present embodiment can be usedas an additive in a non-aqueous electrolytic solution for a powerstorage element. In this case, the non-aqueous electrolytic solution isconfigured by adding at least one phosphodiester salt, as an additive,to an organic solvent (non-aqueous solvent) containing an electrolytedissolved therein.

In a sodium ion secondary battery as a sort of a power storage element,an irreversible reaction of decomposition of a non-aqueous electrolyticsolution arises at an interface between electrodes and the non-aqueouselectrolytic solution, at an initial time of charging the secondarybattery. In accordance with the kind of electrode active materials, thekind of a non-aqueous solvent, an electrolyte and an additive in thenon-aqueous electrolytic solution, and charge-discharge conditions,properties of a film to be formed, for example, thermal stability, ionconductivity, morphology, and denseness will significantly vary. Also inthe present embodiment, a film is formed on each surface of electrodeactive materials by adding the phosphoric acid diester salt to thenon-aqueous electrolytic solution as an additive. The effect ofproperties of this film, that is, thermal stability, film quality andthe like can suppress charge-discharge characteristics of the sodium ionsecondary from deteriorating and suppress the internal resistance fromrising even after storage under high temperature environment (forexample, 40° C. to 100° C.).

Regarding the sentence that the non-aqueous electrolytic solution for apower storage element of the present embodiment contains a “phosphoricacid diester salt as an additive”, the phosphoric acid diester salt isused together with a main electrolyte in the non-aqueous electrolyticsolution for a power storage element, and the additive means a compoundwhich is added for the purpose of suppressing deterioration ofcharge-discharge characteristics of the power storage element, andsuppressing the rise in internal resistance after storage at hightemperature, leading to an improvement in battery characteristics.

The additive amount of the phosphodiester salt as the additive ispreferably in a range of 0.005 to 5% by mass, more preferably 0.01 to 3%by mass, and still more preferably 0.15 to 1.5% by mass, based on thetotal mass of the non-aqueous electrolytic solution. When the additiveamount is set at 0.005% by mass or more, it is possible to suppresscharge-discharge characteristics from deteriorating and to suppress therise in internal resistance even after exposing the secondary battery tohigh temperature environment. Meanwhile, when the additive amount is setat 5% by mass or less, it is possible to suppress the solubility of theelectrolyte in the non-aqueous electrolytic solution from being lowered.

<Electrolyte>

It is possible to employ, as the above electrolyte, conventionally knownelectrolytes used in various power storage elements. When theelectrolyte is for lithium ion batteries, the electrolyte may be alithium salt. For example, when the power storage element is a sodiumion secondary battery, a sodium salt can be used.

The electrolyte is preferably an electrolyte which contains an anioncontaining fluorine. Specific examples of such a fluorine-containinganion include BF₄ ⁻, PF₆ ⁻, BF₃CF₃ ⁻, BF₃C₂F₅ ⁻, CF₃SO₃ ⁻, C₂F₅SO₃ ⁻,C₃F₇SO₃ ⁻, C₄F₉SO₃ ⁻, N(SO₂F)₂ ⁻, N(CF₃SO₂)₂ ⁻, N(C₂F₅SO₂)₂ ⁻,N(CF₃SO₂)(CF₃CO)⁻, N(CF₃SO₂)(C₂F₅SO₂)⁻, C(CF₃SO₂)₃ ⁻ and the like. Theseelectrolytes can be used alone or in combination of two or more thereof.Among fluorine-containing anions, BF₄ ⁻, PF₆ ⁻, and N(CF₃SO₂)₂ ⁻ arepreferred, and BF₄ ⁻, PF₆ ⁻ are particularly preferred, from theviewpoint of improvement in safety/stability and electric conductivityof the non-aqueous electrolytic solution, and the cycle characteristics.

The concentration of the electrolyte in the organic solvent is notparticularly limited, and is usually in a range of 0.1 to 2 M,preferably 0.15 to 1.8 M, more preferably 0.2 to 1.5 M, and particularlypreferably 0.3 to 1.2 M. When the concentration is set at 0.1 M or more,it is possible to prevent the electric conductivity of the non-aqueouselectrolytic solution from becoming insufficient. Meanwhile, when theconcentration is set at 2 M or less, it is possible to suppress theelectric conductivity from deteriorating due to the rise in viscosity ofthe non-aqueous electrolytic solution, thus making it possible toprevent secondary battery performance from deteriorating.

<Organic Solvent>

Examples of the organic solvent (non-aqueous solvent) used in thenon-aqueous electrolytic solution include, but are not limited to,cyclic carbonate, chain carbonate, phosphate, cyclic ether, chain ether,lactone compound, chain ester, nitrile compound, amide compound, sulfonecompound and the like. Among these organic solvents, carbonates arepreferred from the viewpoint of being commonly used as an organicsolvent for secondary batteries.

Examples of the cyclic carbonate include, but are not limited to,ethylene carbonate, propylene carbonate, butylene carbonate and thelike. Among these, cyclic carbonates such as ethylene carbonate andpropylene carbonate are preferred in view of improving the chargeefficiency of the sodium ion secondary battery. Examples of the chaincarbonate include, but are not limited to, dimethyl carbonate,ethylmethyl carbonate, diethyl carbonate and the like. Among these,dimethyl carbonate and ethylmethyl carbonate are preferred in view ofimproving the charge efficiency of the sodium ion secondary battery.Examples of the phosphate include, but are not limited to, trimethylphosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethylphosphate and the like. Examples of the cyclic ether include, but arenot limited to, tetrahydrofuran, 2-methyltetrahydrofuran and the like.Examples of the chain ether include, but are not limited todimethoxyethane. Examples of the lactone compound include, but are notlimited to, γ-butyrolactone. Examples of the chain ester include, butare not limited to, methyl propionate, methyl acetate, ethyl acetate,methyl formate and the like. Examples of the nitrile compound include,but are not limited to, acetonitrile. Examples of the amide compoundinclude, but are not limited to, dimethylformamide Examples of thesulfone compound include, but are not limited to, sulfolane,methylsulfolane and the like. It is also possible to suitably use thoseobtained by partially substituting hydrogens of a hydrocarbon groupcontained in the above organic solvent molecules with fluorine. Theseorganic solvents may be used alone or in the form of a mixture of two ormore thereof. From the viewpoint of availability and performances,carbonates are preferably used as the organic solvent.

<Method for Producing Non-Aqueous Electrolytic Solution>

The non-aqueous electrolytic solution of the present embodiment can beobtained by adding a salt of the above electrolyte to the above organicsolvent (non-aqueous solvent) and adding a phosphoric acid diester saltas an additive. In this case, it is preferred to use, as the organicsolvent, a salt of an electrolyte, phosphoric acid diester salt, andother additives to be added optionally, those in which impurities arereduced as much as possible by purifying in advance as long as theproductivity of the non-aqueous electrolytic solution does notdeteriorate.

<Others>

Conventionally known other additives may be added to the non-aqueouselectrolytic solution according to the present embodiment.

(Electrolyte for Non-Aqueous Electrolytic Solution of Power StorageElement)

The phosphoric acid diester salt of the present embodiment can also beused as an electrolyte in a non-aqueous electrolytic solution of a powerstorage element. In this case, the non-aqueous electrolytic solution isconfigured by optionally including a known additive and a knownelectrolyte in an organic solvent (non-aqueous solvent) containing anelectrolyte dissolved therein.

When using as the electrolyte, the concentration of the phosphoric aciddiester salt in the organic solvent is not particularly limited, and isusually in a range of 0.1 to 2M, preferably 0.15 to 1.8M, morepreferably 0.2 to 1.5M, and particularly preferably 0.3 to 1.2M. Whenthe concentration is set at 0.1 M or more, it is possible to prevent theelectric conductivity of the non-aqueous electrolytic solution frombecoming insufficient and to suppress charge-discharge characteristicsof the sodium ion secondary from deteriorating, and to suppress theinternal resistance from rising even after storage under hightemperature environment. Meanwhile, when the concentration is set at 2 Mor less, it is possible to suppress the electric conductivity fromdeteriorating due to deterioration of the solubility in the non-aqueouselectrolytic solution and the rise in viscosity of the non-aqueouselectrolytic solution, thus making it possible to prevent theperformance of the power storage element from deteriorating.

<Organic Solvent>

It is possible to use, as the organic solvent, organic solvents whichare the same as those described in the case where the phosphoric aciddiester salt of the present embodiment is used as an additive, withoutlimitation.

<Production of Non-Aqueous Electrolytic Solution>

When using the phosphoric acid diester salt as an electrolyte, thenon-aqueous electrolytic solution is obtained, for example, by adding aphosphoric acid diester salt to the above organic solvent (non-aqueoussolvent) and optionally adding a known additive and a known electrolyte.In this case, it is preferred to use, as the organic solvent, aphosphoric acid diester salt, and other additives to be addedoptionally, those in which impurities are reduced as much as possible bypurifying in advance as long as the productivity of the non-aqueouselectrolytic solution does not deteriorate.

(Power Storage Element)

Examples of the power storage element of the present embodiment includea sodium ion secondary battery, a lithium ion secondary battery, anelectric double layer capacitor and the like. The phosphoric aciddiester salt of the present embodiment can be suitably used as anadditive for a non-aqueous electrolytic solution and an electrolyte tothese various power storage elements.

<Sodium Ion Secondary Battery>

When the power storage element is, for example, a sodium ion secondarybattery, the following configuration can be employed. FIG. 1 is aschematic sectional view that schematically illustrates a sodium ionsecondary battery with the above non-aqueous electrolytic solution.

As illustrated in FIG. 1, the sodium ion secondary battery according tothe present embodiment has a structure in which in an internal spaceformed by a positive electrode can 4 and a negative electrode can 5, astacked body is held and, in the stacked body, from the positiveelectrode can 4-side of the body, a positive electrode 1, a separator 3,a negative electrode 2, and a spacer 7 are stacked in this order. Byinterposing a spring 8 between the negative electrode can 5 and theseparator 7, the positive electrode 1 and the negative electrode 2 canbe pressed and bonded to each other in an appropriate degree to be fixedto each other. The positive electrode 1, the separator 3, and thenegative electrode 2 are impregnated with the non-aqueous electrolyticsolution, which contains a phosphoric acid diester salt, in the presentembodiment. By putting the positive electrode can 4 and the negativeelectrode can 5 onto each other in the state of interposing a gasket 6between the positive electrode can 4 and the negative electrode can 5,the both are bonded to each other so that the stacked body comes into anairtightly sealed state.

In the case of the sodium ion secondary battery, examples of thematerial of the positive electrode active material layer in the positiveelectrode 1 include, but are not limited to, a transition metal compoundin which sodium ion has a diffusible structure, or an oxide of thetransition metal compound and sodium. Specific examples thereof includeNaFeO₂, NaNiO₂, NaCoO₂, NaMnO₂, NaVO₂, NaCrO₂,Na_(0.7)(Mn_(x)Ni_(y)Co_(z))O₂ (x+y+z=1, 0<x≤1, 0<y≤1, 0<z≤1),Na_(2/3)(Ni_(x)Mn_(y))O₂ (x+y=1, 0<x≤1, 0<y≤1), Na_(2/3)(Fe_(x)Mn_(y))O₂(x+y=1, 0<x≤1, 0<y≤1), Na_(2/3)(Ni_(x)Mn_(y)Mg_(z))O₂ (x+y+z=1, 0<x≤1,0<y≤1, 0<z≤1), Na_(2/3)(Ni_(x)Mn_(y)Al_(z))O₂ (x+y+z=1, 0<x≤1, 0<y≤1,0<z≤1), Na₂Fe₂P₂O₇, Na₃V₂(PO₄)₃, Na₄Ni₃(PO₄)₂P₂O₇, Na₄Co₃(PO₄)₂P₂O₇,Na₂Fe₂(SO₄)₃ and the like.

The positive electrode 1 can be obtained by press-molding the positiveactive materials listed up above together with a known conducting aidand a known binder, or by mixing the positive active material, togetherwith a known conducting aid and a known binder, in an organic solventsuch as pyrrolidone to prepare a paste, and applying the paste onto acurrent collector such as an aluminum foil, followed by drying.

In the case of a sodium ion battery, the material of a negative activematerial layer in the negative electrode 2 is not particularly limitedas long as the material can store and release lithium. Examples thereofinclude metal sodium; metal oxide such as Na₂Ti₆O₁₃; and carbonmaterials such as natural graphite, artificial graphite, graphiteboride, hard carbon, meso-carbon microbeads, pitch type carbon fiber,graphitized products, and carbon nanotubes.

The negative electrode 2 may be an electrode in the form of a foil orpowder of the above electrode materials. In the case of the powderynegative electrode, this negative electrode can be obtained bypress-molding the negative electrode material together with a knownconducting aid and a known binder, or by mixing the material, togetherwith a known conducting aid and a known binder, in an organic solventsuch as pyrrolidone to prepare a paste, and applying the paste onto acurrent collector such as a copper foil, followed by drying.

In the sodium ion secondary battery according to the present embodiment,between the positive electrode 1 and the negative electrode 2, theseparator 3 is usually interposed in order to prevent these electrodesfrom being short-circuited. The material and the shape of the separator3 are not particularly limited. The material is preferably anelectrically-insulating chemically-stable material through which theabove-mentioned non-aqueous electrolytic solution is easy to pass. Theseparator 3 is, for example, a microporous film or sheet made of variouspolymeric materials. Specific examples of the polymeric material includenylon (registered trademark), nitrocellulose, polyacrylonitrile,polyvinylidene fluoride, and polyolefin polymers such as polyethyleneand polypropylene. From the viewpoint of electrochemical stability andchemical stability, polyolefin polymers are preferred.

An optimal use voltage for the sodium ion secondary battery of thepresent embodiment varies in accordance with the combination of thepositive electrode 1 with the negative electrode 2. Usually, the sodiumion secondary battery is usable at an average discharge voltage in arange of 2.4 to 4.5 V.

Examples of the form of the sodium ion secondary battery of the presentembodiment include, but are not limited to, a cylindrical form, arectangular form, a laminate form and the like, in addition to thecoin-shaped cell illustrated in FIG. 1.

The sodium ion secondary battery according to the present embodiment cansuppress deterioration of charge-discharge characteristics and the risein internal resistance after storage in temperature load environment.Thus, the non-aqueous electrolytic solution of the present embodiment issuitably usable for sodium ion secondary batteries. The sodium ionsecondary battery illustrated in FIG. 1 is an example, but the secondarybattery of the invention is not limited thereto.

<Electric Double Layer Capacitor>

With respect to the case where the power storage element is an electricdouble layer capacitor, the same configuration as that of the sodium ionsecondary battery can be employed. Specifically, an electric doublelayer capacitor can employ the structure in which, as illustrated inFIG. 1, in an internal space formed by a positive electrode can 4 and anegative electrode can 5, a stacked body is held and, in the stackedbody, from the positive electrode can 4-side of the body, a positiveelectrode 1, a separator 3, a negative electrode 2, and a spacer 7 arestacked in this order. The positive electrode 1, the negative electrode2, and the separator 3 are impregnated with the non-aqueous electrolyticsolution containing a phosphoric acid diester salt of the presentembodiment.

The positive electrode 1 and the negative electrode 2 can be obtained bypress-molding the below-mentioned active carbon together with a knownconducting aid and a known binder. The positive electrode 1 and thenegative electrode 2 can also be obtained by mixing the positive activematerials listed up above together with a known conducting aid and aknown binder, in an organic solvent such as pyrrolidone to prepare apaste, and applying the paste onto a current collector such as analuminum foil, followed by drying.

The active carbon is not particularly limited, and it is possible to usea known active carbon which is usually used. The specific surface areaof the active carbon is not particularly limited, but is usually in arange of 1,000 m²/g to 3,000 m²/g, and preferably 1,000 m²/g to 2,000m²/g.

Examples of the material of active carbon include, but are not limitedto, carbonaceous raw materials such as lumber, coconut shell, sawdust,coal, pitch, coke, phenol resin, furan resin, polyvinyl chloride resin,polyvinylidene chloride resin, polyimide resin, polyamide resin,polycarbodiimide resin, waste plastic, and waste tire.

The active carbon is obtained by carbonizing the carbonaceous rawmaterials listed up above at a temperature of 900° C. or lower, followedby subjecting to an activation treatment. Examples of the activationmethod include, but are not limited to, a gas activation method, achemical activation method and the like. In the case of the gasactivation method, active carbon can be obtained by a catalytic reactionof a carbonated raw material with an oxidation gas such as water vapor,carbon dioxide, or oxygen at high temperature in a range of 600° C. to1,000° C. In the case of the chemical activation method, active carboncan be obtained by mixing a carbonized raw material with a chemical suchas zinc chloride, phosphoric acid, sodium phosphate, calcium chloride,potassium sulfide, potassium hydroxide, sodium hydroxide, potassiumcarbonate, sodium carbonate, sodium sulfate, potassium sulfate, calciumcarbonate, boric acid, or nitric acid, and heating to arbitrarytemperature in an inert atmosphere to thereby perform adehydration/oxidation reaction of the chemical. By performing theseactivation treatments, active carbon formed with numerous pores can beobtained, thus making it possible to increase a specific surface areathereof.

EXAMPLES

Preferred examples of the present invention will be illustrativelydescribed in detail below. However, about materials, mixing amounts andothers mentioned in the Examples, the scope of the present invention isnot limited only to these described matters unless the specificationespecially includes a restrictive description thereabout.

Example 1 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In a 200 mL beaker, 15 g of 2,2,2-trifluoroethanol, 14 g oftriethylamine, and 100 g of dimethoxyethane were charged. Whilestirring, a solution prepared by diluting 10 g of ethyldichlorophosphate to 50% with 10 g of dimethoxyethane was slowly addeddropwise at room temperature. It was verified that heat is graduallygenerated during dropwise addition, and a white precipitate isprecipitated in the system. Thereafter, stirring was performed at roomtemperature for 1 hour. The white precipitate was then separated into awhite solid and a filtrate by performing filtration under reducedpressure. Thereafter, dimethoxyethane was distilled off from thefiltrate under reduced pressure. Subsequently, the thus obtained liquidwas repeatedly washed three times by adding water, and the liquid in thelower layer was isolated to obtain 14 g of ethylbis(2,2,2-trifluoroethyl)phosphate as a colorless transparent liquid.

Synthesis of sodium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 4.2 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueoussodium hydroxide solution was charged. The aqueous sodium hydroxidesolution is prepared by dissolving 0.56 g of sodium hydroxide in 5.0 gof water. Thereafter, while stirring, the mixture was heated underreflux at 100° C. to 110° C. for 1 hour. The solvent was distilled offunder reduced pressure at 80° C. to obtain 2.6 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected. Thus, it was verified that novel anions areproduced. Furthermore, the thus obtained white solid was subjected tonegative ion analysis using LC/MS (manufactured by Waters Corporation).As a result, a mass peak was observed at m/z=207.1. Since thisapproximately corresponds with the molecular weight ofethyl(2,2,2-trifluoroethyl)phosphoric acid anion, it was verified thatthe thus obtained white solid is sodiumethyl(2,2,2-trifluoroethyl)phosphate. The m/z means a mass-to-chargeratio, m represents the mass of ions, and z represents the charge numberof ions.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

Inside a dry box having an argon atmosphere having a dew point of −70°C. or lower, a non-aqueous electrolytic solution was prepared to set theconcentration of NaPF₆ at 1.0 mol/liter in propylene carbonate (PC)(sodium battery grade, manufactured by Kishida Chemical Co., Ltd.).Furthermore, a preparation was made to set the addition amount of thesodium ethyl(2,2,2-trifluoroethyl)phosphate at 0.5% by mass of the wholemass of the non-aqueous electrolytic solution. In this way, anon-aqueous electrolytic solution for sodium ion secondary batteries,which contains sodium ethyl(2,2,2-trifluoroethyl)phosphate as anadditive, of the present example was prepared.

Example 2 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of potassium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 10.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueoussolution prepared by dissolving 1.8 g of potassium hydroxide in 5.0 g ofwater was charged. Thereafter, while stirring, the mixture was heatedunder reflux at 100° C. to 110° C. for 1 hour. The solvent was distilledoff under reduced pressure at 80° C. to obtain 7.2 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is potassiumethyl(2,2,2-trifluoroethyl)phosphate.

Example 3 Synthesis of ethyl(2,2,2-trifluoroethyl)phosphoric acid

In a 50 mL recovery flask, 4.0 g of potassiumethyl(2,2,2-trifluoroethyl)phosphate synthesized in Example 2 wascharged and then hydrochloric acid was charged. The charged hydrochloricacid is prepared by mixing 2.7 g of hydrochloric acid having theconcentration of 37% with 10.0 g of water. Thereafter, stirring wasperformed at room temperature for 15 minutes. Subsequently, solventextraction was performed using 25 mL of diethyl ether as an extractionsolvent. The solvent extraction was performed four times. Thereafter,diethyl ether was distilled off under reduced pressure at 40° C. toobtain 3.3 g of a colorless transparent liquid.

The thus obtained colorless transparent liquid was subjected to anionanalysis using ion chromatography <IC-850, manufactured by Metrohm AG>.As a result, one novel peak was detected at the same detection time asthat of the sodium ethyl(2,2,2-trifluoroethyl)phosphate. Thus, it wasverified that the thus produced novel anion isethyl(2,2,2-trifluoroethyl)phosphoric acid anion, and the thus obtainedcolorless transparent liquid is ethyl(2,2,2-trifluoroethyl)phosphoricacid.

Example 4 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of calcium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 1.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueouscalcium hydroxide solution was charged. The aqueous sodium hydroxidesolution is composed of a suspension prepared by adding 10.0 g of waterto 0.1 g of calcium hydroxide. Thereafter, while stirring, the mixturewas heated under reflux at 100° C. to 110° C. for 2 hours. Furthermore,the solvent was distilled off under reduced pressure at 80° C. to obtain0.6 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is calciumethyl(2,2,2-trifluoroethyl)phosphate.

Example 5 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of magnesium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 6.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueousmagnesium hydroxide solution was charged. The aqueous magnesiumhydroxide solution is composed of a suspension prepared by adding 15.0 gof water to 0.6 g of magnesium hydroxide. Thereafter, while stirring,the mixture was heated under reflux at 100° C. to 110° C. for 10 hours.Furthermore, the solvent was distilled off under reduced pressure at 80°C. to obtain 4.2 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is magnesiumethyl(2,2,2-trifluoroethyl)phosphate.

Example 6 Synthesis of ethyl bis(2-(2-(2-methoxyethoxy)ethoxy))phosphate

In a 200 mL beaker, 20.6 g of triethylene glycol monomethyl ether, 12.4g of triethylamine, and 100 g of dimethoxyethane were charged. Whilestirring, a solution prepared by diluting 10 g of ethyldichlorophosphate to 50% with 10 g of dimethoxyethane was slowly addeddropwise at room temperature. It was verified that heat is graduallygenerated during dropwise addition, and a white precipitate isprecipitated in the system. Thereafter, stirring was performed at roomtemperature for 1 hour. The white precipitate was then separated into awhite solid and a filtrate by performing filtration under reducedpressure. Thereafter, dimethoxyethane was distilled off from thefiltrate under reduced pressure. Subsequently, the thus obtained liquidwas dissolved by adding dimethoxyethane, and purified by subjecting toflash chromatography using a silica gel to obtain 20.5 g of ethylbis(2-(2-(2-methoxyethoxy)ethoxy))phosphate as a colorless transparentliquid.

Synthesis of sodium ethyl(2-(2-(2-methoxyethoxy)ethoxy))phosphate

In a 50 mL recovery flask, 10 g of the ethylbis(2-(2-(2-methoxyethoxy)ethoxy))phosphate was charged and then anaqueous sodium hydroxide solution was charged. The aqueous sodiumhydroxide solution is prepared by dissolving 0.91 g of sodium hydroxidein 10 g of water. Thereafter, while stirring, the mixture was heatedunder reflux at 100° C. to 110° C. for 1 hour. Furthermore, the solventwas distilled off under reduced pressure at 80° C. to obtain 6.7 g of awhite gel-like solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected. Thus, it was verified that novel anions areproduced. Furthermore, the thus obtained white solid was subjected tonegative ion analysis using LC/MS (manufactured by Waters Corporation).As a result, a mass peak was observed at m/z=271.1. Since thisapproximately corresponds with the molecular weight ofethyl(2-(2-(2-methoxyethoxy)ethoxy))phosphoric acid anion, it wasverified that the thus obtained white solid is sodiumethyl(2-(2-(2-methoxyethoxy)ethoxy))phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 7 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of1-ethyl-3-methylimidazoliumethyl(2,2,2-trifluoroethyl)phosphoric acid

In a 200 mL recovery flask, 20.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then 83.9 g of anaqueous 10% 1-ethyl-3-methylimidazolium hydroxide solution was charged.Thereafter, while stirring, the mixture was heated under reflux at 100°C. to 110° C. for 1 hour. Furthermore, the solvent was distilled offunder reduced pressure at 80° C. to obtain 19.5 g of an oily pale yellowtransparent liquid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is1-ethyl-3-methylimidazoliumethyl(2,2,2-trifluoroethyl)phosphoric acid.

Example 8 Synthesis of Ethyl Bishexafluoroisopropyl Phosphate

In a 200 mL beaker, 9.9 g of hexafluoroisopropyl alcohol, 5.5 g oftriethylamine, and 100 g of dimethoxyethane were charged. Whilestirring, 4.0 g of ethyl dichlorophosphate was slowly added dropwise atroom temperature. It was verified that heat is gradually generatedduring dropwise addition, and a white precipitate is precipitated in thesystem. Thereafter, stirring was performed at room temperature for 1hour. The white precipitate was then separated into a white solid and afiltrate by performing filtration under reduced pressure. Thereafter,dimethoxyethane was distilled off from the filtrate under reducedpressure. Subsequently, the thus obtained liquid was repeatedly washedthree times by adding water, and the liquid in the lower layer wasisolated to obtain 9.1 g of ethylbis(1,1,1,3,3,3-hexafluoroisopropyl)phosphate as a colorless transparentliquid.

<Synthesis of Sodium Ethyl Hexafluoroisopropyl Phosphate>

In a 50 mL recovery flask, 5.0 g of the ethyl bishexafluoroisopropylphosphate was charged and then an aqueous sodium hydroxide solution wascharged. The aqueous sodium hydroxide solution is prepared by dissolving0.46 g of sodium hydroxide in 5.0 g of water. Thereafter, whilestirring, the mixture was heated under reflux at 100° C. to 110° C. for1 hour. Furthermore, the solvent was distilled off under reducedpressure at 80° C. to obtain 2.5 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected. Thus, it was verified that novel anions areproduced. Furthermore, the thus obtained white solid was subjected tonegative ion analysis using LC/MS (manufactured by Waters Corporation).As a result, a mass peak was observed at m/z=274.9. Since thisapproximately corresponds with the molecular weight ofethylhexafluoroisopropylphosphoric acid anion, it was verified that thethus obtained white solid is sodium ethyl hexafluoroisopropyl phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 9 Synthesis of Ethyl Dimethyl Phosphate

In a 500 mL beaker, 7.4 g of methanol, 20.5 g of triethylamine, and 200g of dimethoxyethane were charged. While stirring, 15.0 g of ethyldichlorophosphate was slowly added dropwise at room temperature. It wasverified that heat is gradually generated during dropwise addition, anda white precipitate is precipitated in the system. Thereafter, stirringwas performed at room temperature for 1 hour. The white precipitate wasthen separated into a white solid and a filtrate by performingfiltration under reduced pressure. Thereafter, dimethoxyethane wasdistilled off from the filtrate under reduced pressure. Subsequently,the thus obtained liquid was dissolved by adding ethyl acetate, andpurified by subjecting to flash chromatography using ethyl acetate and asilica gel to obtain 10.0 g of ethyl dimethyl phosphate as a colorlesstransparent liquid.

<Synthesis of Sodium Ethyl Methyl Phosphate>

In a 50 mL recovery flask, 4.0 g of the ethyl dimethyl phosphate wascharged and then an aqueous sodium hydroxide solution was charged. Theaqueous sodium hydroxide solution is prepared by dissolving 1.0 g ofsodium hydroxide in 5.0 g of water. Thereafter, while stirring, themixture was heated under reflux at 100° C. to 110° C. for 1 hour.Furthermore, the solvent was distilled off under reduced pressure at 80°C. to obtain 3.8 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected. Thus, it was verified that novel anions areproduced. Furthermore, the thus obtained white solid was subjected tonegative ion analysis using LC/MS (manufactured by Waters Corporation).As a result, a mass peak was observed at m/z=138.9. Since thisapproximately corresponds with the molecular weight ofethylmethylphosphoric acid anion, it was verified that the thus obtainedwhite solid is sodium ethyl dimethyl phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 10 <Synthesis of Lithium Ethyl Methyl Phosphate>

In a 50 mL recovery flask, 5.0 g of the ethyl dimethyl phosphate wascharged and then an aqueous solution prepared by dissolving 1.3 g oflithium hydroxide monohydrate in 15.0 g of water was charged.Thereafter, while stirring, the mixture was heated under reflux at 100°C. to 110° C. for 1 hour. Furthermore, the solvent was distilled offunder reduced pressure at 80° C. to obtain 3.0 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected. Thus, it was verified that novel anions areproduced. Furthermore, the thus obtained white solid was subjected tonegative ion analysis using LC/MS (manufactured by Waters Corporation).As a result, a mass peak was observed at m/z=138.9. Since thisapproximately corresponds with the molecular weight ofethyldimethylphosphoric acid anion, it was verified that the thusobtained white solid is lithium ethyl dimethyl phosphate.

Example 11

In the present example, the addition amount of sodiumethyl(2,2,2-trifluoroethyl)phosphate of Example 1 was changed to 0.1% bymass based on the total mass of the non-aqueous electrolytic solution.In the same manner as in Example 1, except for the others, a non-aqueouselectrolytic solution for sodium ion secondary batteries was prepared.

Example 12

In the present example, the addition amount of sodiumethyl(2,2,2-trifluoroethyl)phosphate of Example 1 was changed to 5.0% bymass based on the total mass of the non-aqueous electrolytic solution.In the same manner as in Example 1, except for the others, a non-aqueouselectrolytic solution for sodium ion secondary batteries was prepared.

Example 13

In the present example, the addition amount ofethyl(2,2,2-trifluoroethyl)phosphoric acid of Example 3 was changed to0.1% by mass based on the total mass of the non-aqueous electrolyticsolution. In the same manner as in Example 3, except for the others, anon-aqueous electrolytic solution for sodium ion secondary batteries wasprepared.

Example 14 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of sodium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 5.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueoussodium hydroxide solution was charged. The aqueous sodium hydroxidesolution is prepared by dissolving 0.3 g of sodium hydroxide in 5.0 g ofwater. Thereafter, while stirring, the mixture was heated under refluxat 100° C. to 110° C. for 1 hour. Furthermore, the solvent was distilledoff under reduced pressure at 80° C. to obtain a white solid.Subsequently, the thus obtained white solid was suspended in 10.0 g ofdimethyl carbonate, followed by filtration to obtain 1.6 g of a whitesolid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is sodiumethyl(2,2,2-trifluoroethyl)phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 15 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of sodium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 5.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueoussolution prepared by dissolving 0.7 g of sodium hydroxide in 5.0 g ofwater was charged. Thereafter, while stirring, the mixture was heatedunder reflux at 100° C. to 110° C. for 1 hour. Furthermore, the solventwas distilled off under reduced pressure at 80° C. to obtain 3.9 g of awhite solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is sodiumethyl(2,2,2-trifluoroethyl)phosphate.

<Preparation Non-Aqueous Electrolytic Solution for Sodium Ion SecondaryBatteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 16 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of sodium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 5.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then 30.0 g ofdimethoxyethane was charged as a reaction solvent. Thereafter, anaqueous solution prepared by dissolving 0.7 g of sodium hydroxide in 1.2g of water was charged. Thereafter, while stirring, the mixture washeated under reflux at 100° C. to 110° C. for 1 hour. Furthermore, thesolvent was distilled off under reduced pressure at 80° C. to obtain 3.9g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is sodiumethyl(2,2,2-trifluoroethyl)phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Example 17 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of sodium ethyl(2,2,2-trifluoroethyl)phosphate

In a 50 mL recovery flask, 20.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then an aqueoussolution prepared by dissolving 0.6 g of sodium hydroxide in 1.2 g ofwater was charged. Thereafter, while stirring, the mixture was heatedunder reflux at 100° C. to 110° C. for 1 hour. Furthermore, the solventand the solid were filtered to obtain a white solid. The solvent wasdistilled off from the thus obtained white solid under reduced pressureat 80° C. to obtain 2.2 g of a white solid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is sodiumethyl(2,2,2-trifluoroethyl)phosphate.

<Preparation of Non-Aqueous Electrolytic Solution for Sodium IonSecondary Batteries>

In the same manner as in Example 1, a non-aqueous electrolytic solutionfor sodium ion secondary batteries according to the present example wasprepared.

Comparative Example 1

In the same manner as in Example 1, except that sodiumethyl(2,2,2-trifluoroethyl)phosphate of Example 1 was not added in thepresent comparative example, a non-aqueous electrolytic solution forsodium ion secondary batteries was prepared.

(Evaluation of Electrochemical Characteristics of Sodium Ion SecondaryBattery)

Electrochemical characteristics of sodium ion secondary batteries usingeach of non-aqueous electrolytic solutions of Examples 1, 6, 8, 9, and11 to 17 and Comparative Example 1 were evaluated. In the evaluation, athree-electrode type evaluation cell illustrated in FIG. 2 was used.

<Assembling of Sodium Ion Secondary Battery>

A glass container 15 with a Teflon (registered trademark) lid 14 in theevaluation cell illustrated in FIG. 2 was filled with each of thenon-aqueous electrolytic solutions obtained in Examples and ComparativeExample 1. A working electrode 17 was supported by a stainless steelsupporting rod 11 for a working electrode; a reference electrode 18 wassupported by a stainless steel supporting rod 12 for a referenceelectrode; and a counter electrode 19 was supported by a stainless steelsupporting rod 13 for a counter electrode.

The following electrodes were used as the working electrode 17. That is,an electrode, which is obtained by making NaCrO₂ together with an activematerial, a conducting aid and a binder into a paste form, applying thepaste onto a current collector made of an aluminum foil, drying thepaste, making the dried paste into a sheet form, and then cutting outthe sheet into a 1-cm square piece, was used as a working electrode 17.Regarding the reference electrode 18 and the counter electrode 19, asodium foil was used notwithstanding whether the positive or negativeelectrode material was to be evaluated.

The stainless steel supporting rod 11 for the working electrode, thestainless steel supporting rod 12 for the reference electrode, and thestainless steel supporting rod 13 for the counter electrode were fixedthrough the Teflon lid 14. The Teflon lid was fitted to the glasscontainer 15 in which a non-aqueous electrolytic solution 16 was added.Simultaneously, the working electrode 17, the reference electrode 18 andthe counter electrode 19 were simultaneously immersed in the non-aqueouselectrolytic solution 16.

The glass container 15 was inserted and fitted into an aluminum block10, the temperature of the block 10 being controllable, to adjust thetemperature of the inside of the glass container 15.

As an electrochemical measuring instrument, PGSTAT302N manufactured byMetrohm Autolab was used to carry out cyclic voltammetry measurementsand AC impedance measurements. All operations from assembling of theevaluation cell to the measurements were made in the argon glove box,which had a dew point of −70° C. or lower.

<Evaluation of Positive Electrode Material of Sodium Ion SecondaryBattery>

After the temperature of the non-aqueous electrolytic solution was keptat 25° C., the cyclic voltammetry measurements were performed at a sweeprate of 1 mV/second from the immersion potential to 3,400 mV. Thedischarge capacity in the 5th cycle when using the non-aqueouselectrolytic solution of Comparative Example 1 was regarded as 100, andthe ratio of the charge capacity in the 5th cycle when using each of thenon-aqueous electrolytic solutions of Examples 1, 6, 8, 9, and 11 to 17is shown in Table 1 below.

TABLE 1 Addition Discharge amount of capacity ratio Non-aqueouselectrolytic solution additive (% at 25° C. after Electrolyte Additiveby mass) 5 cycles Example1 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 0.5 120 Example 6 NaPF₆ Sodium 0.5115 ethyl(2-(2-(2-methoxyethoxy)ethoxy))phosphate Example 8 NaPF₆ Sodiumethyl hexafluoroisopropyl phosphate 0.5 113 Example 9 NaPF₆ Sodium ethylmethyl phosphate 0.5 116 Example 11 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 0.1 115 Example 12 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 5.0 124 Example 13 NaPF₆ethyl(2,2,2-trifluoroethyl)phosphoric acid 0.1 111 Example 14 NaPF₆Sodium ethyl(2,2,2-trifluoroethyl)phosphate 0.5 120 Example 15 NaPF₆Sodium ethyl(2,2,2-trifluoroethyl)phosphate 0.5 121 Example 16 NaPF₆Sodium ethyl(2,2,2-trifluoroethyl)phosphate 0.5 121 Example 17 NaPF₆Sodium ethyl(2,2,2-trifluoroethyl)phosphate 0.5 120 Comparative NaPF₆ —— 100 Example 1

<Evaluation of Positive Electrode Internal Resistance of Sodium IonSecondary Battery>

Subsequently, while the temperature of the non-aqueous electrolyticsolution was kept at 25° C., the battery was charged to 3,400 mV at acharge current of 0.7 mA. Thereafter, the battery was kept at 3,400 mVfor 3 hours. Thereafter, while the application of the voltage of 3,400mV was kept as it was, the temperature was raised to 60° C., followed bykeeping at 60° C. for 5 hours. Thereafter, the temperature was loweredto 0° C. step by step, and the AC impedance was measured, followed bycomparison and evaluation about the electrode resistance. The resistanceat 0° C. when using the non-aqueous electrolytic solution of ComparativeExample 1 was regarded as 100, and the ratio of the internal resistanceof the positive electrode in each non-aqueous electrolytic solution ofExample 1 is shown in Table 2 below.

TABLE 2 Internal resistance ratio Non-aqueous electrolytic solution at60° C. Electrolyte Additive after 5 hours Example 1 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 72 Example 6 NaPF₆ Sodiumethyl(2-(2-(2-methoxyethoxy)ethoxy))phosphate 87 Example 8 NaPF₆ Sodiumethyl hexafluoroisopropyl phosphate 91 Example 9 NaPF₆ Sodium ethylmethyl phosphate 88 Example 11 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 90 Example 12 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 74 Example 13 NaPF₆ethyl(2,2,2-trifluoroethyl)phosphoric acid 92 Example 14 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 73 Example 15 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 70 Example 16 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 69 Example 17 NaPF₆ Sodiumethyl(2,2,2-trifluoroethyl)phosphate 71 Comparative NaPF₆ — 100 Example1

Example 18 Synthesis of ethyl bis(2,2,2-trifluoroethyl)phosphate

In the same manner as in Example 1, ethylbis(2,2,2-trifluoroethyl)phosphate was synthesized.

Synthesis of triethylmethylammoniumethyl(2,2,2-trifluoroethyl)phosphoric acid

In a 100 mL recovery flask, 20.0 g of the ethylbis(2,2,2-trifluoroethyl)phosphate was charged and then 24.9 g of anaqueous 35% triethylmethylammonium hydroxide solution was charged.Thereafter, while stirring, the mixture was heated under reflux at 100°C. to 110° C. for 1 hour. The solvent was distilled off under reducedpressure at 80° C. to obtain 20.8 g of an oily colorless transparentliquid.

The thus obtained white solid was subjected to anion analysis using ionchromatography <IC-850, manufactured by Metrohm AG>. As a result, onenovel peak was detected at the same detection time as that of the sodiumethyl(2,2,2-trifluoroethyl)phosphate. Thus, it was verified that thethus produced novel anion is ethyl(2,2,2-trifluoroethyl)phosphoric acidanion, and the thus obtained white solid is triethylmethylammoniumethyl(2,2,2-trifluoroethyl)phosphoric acid.

<Preparation of Non-Aqueous Electrolytic Solution for Electric DoubleLayer Capacitor>

Inside a dry box having an argon atmosphere having a dew point of −70°C. or lower, a non-aqueous electrolytic solution was prepared to set theconcentration of triethylmethylammoniumethyl(2,2,2-trifluoroethyl)phosphoric acid synthesized in Example 5 at1.0 mol/liter in propylene carbonate (PC) (sodium battery grade,manufactured by Kishida Chemical Co., Ltd.). Thus, a non-aqueouselectrolytic solution for electric double layer capacitors, whichcontains triethylmethylammonium ethyl(2,2,2-trifluoroethyl)phosphoricacid as an electrolyte, of the present example was prepared.

Comparative Example 2

In the same manner as in Example 18, except that triethylmethylammoniumethyl(2,2,2-trifluoroethyl)phosphoric acid of Example 18 was not addedand the addition was performed such that the concentration oftetraethylammonium tetrafluoroborate became 1.0 mol/liter in the presentcomparative example, a non-aqueous electrolytic solution for electricdouble layer capacitors was prepared.

(Evaluation of Electrochemical Characteristics of Electric Double LayerCapacitor)

Electrochemical characteristics of electric double layer capacitorsusing each of non-aqueous electrolytic solutions of Example 18 andComparative Example 2 were evaluated. In the evaluation, a coin-shapedcell illustrated in FIG. 1 was used.

<Assembling of Electric Double Layer Capacitor>

As the positive electrode 1 and the negative electrode 2 in thecoin-shaped cell, electrodes produced in the following manner were used.That is, an electrode, which is obtained by making active carbon havinga specific surface area of 2,000 m²/g obtained by an activationtreatment through an activation method using water vapor, together withan auxiliary conductive agent and a binder into a paste form, applyingthe paste onto a current collector made of an aluminum foil, drying thepaste, making the dried paste into a sheet form, and then cutting outthe sheet into a 1-cm square piece, was used as a positive electrode 1and a negative electrode 2.

As illustrated in FIG. 1, assembling of the coin-shaped cell wasperformed so that, in an internal space formed by a positive electrodecan 4 and a negative electrode can 5, a stacked body is held in thestacked body in which a positive electrode 1, a separator 3, a negativeelectrode 2, and a spacer 7 are stacked in this order from the positiveelectrode can 4-side of the body. The positive electrode 1, the negativeelectrode 2, and the separator 3 are impregnated with the non-aqueouselectrolytic solution.

As an electrochemical measuring instrument, PGSTAT302N manufactured byMetrohm Autolab was used to carry out cyclic voltammetry measurementsand AC impedance measurements. All operations from assembling of thecoin-shaped cell to the measurements were made in the argon glove box,which had a dew point of −70° C. or lower.

<Evaluation of Positive Electrode Internal Resistance of Electric DoubleLayer Capacitor>

After the temperature of each coin-shaped cell was kept at 25° C., thecell was charged to 3,400 mV at a charge current of 1.0 mA. Thereafter,the battery was kept at 3,000 mV for 10 minutes. Thereafter, the cellwas discharged to 0 mV at a discharge current of 1.0 mV, followed bykeeping at 0 mV for 10 minutes. After performing 5 cycles under thesecharge-discharge conditions, the AC impedance was measured, followed bycomparison and evaluation about the internal resistance of thecapacitor. The resistance when using the non-aqueous electrolyticsolution of Comparative Example 2 was regarded as 100, and the ratio ofthe internal resistance of the positive electrode 1 in the non-aqueouselectrolytic solution of Example 18 is shown in Table 3 below.

TABLE 3 Internal resistance Non-aqueous electrolytic solution ratioafter Electrolyte Additive 5 cycles Example 18 Triethylmethylammonium — 90 ethyl(2,2,2-trifluoroethyl)phosphoric acid ComparativeTriethylmethylammonium tetra- — 100 Example 2 fluoroborate

DESCRIPTION OF REFERENCE SIGNS

-   1 Positive electrode-   2 Negative electrode-   3 Separator-   4 Positive electrode can-   5 Negative electrode can-   6 Gasket-   7 Spacer-   8 Spring-   10 Aluminum block-   11 Stainless steel supporting rod-   12 Stainless steel supporting rod-   13 Stainless steel supporting rod-   14 Teflon lid-   15 Glass container-   16 Non-aqueous electrolytic solution-   17 Working electrode-   18 Reference electrode-   19 Counter electrode

What is claimed is:
 1. A non-aqueous electrolytic solution for a powerstorage element, comprising, as an electrolyte, a phosphoric aciddiester salt represented by the following chemical formula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.
 2. The non-aqueouselectrolytic solution for a power storage element according to claim 1,wherein either one of R¹ and R² is an alkyl group having 1 to 10 carbonatoms and having a halogen atom, and other one is an alkyl group having1 to 10 carbon atoms and having no halogen atom.
 3. The non-aqueouselectrolytic solution for a power storage element according to claim 1,wherein either one of R¹ and R² is a 2,2,2-trifluoroethyl group, and theother one is an ethyl group.
 4. The non-aqueous electrolytic solutionfor a power storage element according to claim 1, wherein M is at leastone selected from the group consisting of lithium, sodium, magnesium,and calcium.
 5. The non-aqueous electrolytic solution for a powerstorage element according to claim 1, wherein M istriethylmethylammonium, tetraethylammonium, 1-ethyl-3-methylimidazolium,or 1-ethyl-2methylpyrrolidinium.
 6. A power storage element using anon-aqueous electrolytic solution comprising, as an electrolyte, aphosphoric acid diester salt represented by the following chemicalformula (1):

wherein M^(n+) represents a hydrogen ion, an alkali metal ion, an alkaliearth metal ion, an aluminum ion, a transition metal ion, or an oniumion; R¹ and R² are different from each other and represent a hydrocarbongroup having 1 to 10 carbon atoms, or a hydrocarbon group having 1 to 10carbon atoms and having at least one of a halogen atom, a heteroatom,and an unsaturated bond; and n represents a valence.